Development of primordial externae in the colonial interna of Polyascus polygenea (Crustacea: Cirripedia: Rhizocephala)

Abstract

We performed a histological investigation of the different stages of development of primordial externae in the interna of Polyascus polygenea Glenner, Lutzen et Takahashi, 2003, a common parasite of an intertidal crab, Hemigrapsus sanguineus (de Haan, 1835). Development of the primordia begins with budding of the interna and the formation of numerous nuclei, i.e. clusters of non-differentiated embryonic cells surrounded by an epithelial layer. The non-differentiated cells of the nuclei undergo intensive mitotic reproduction. After the stage of cell proliferation, the processes of epithelial morphogenesis in the primordial externae and the related anlagen of the trophic system were observed. The primordial ovary in the developing externae already comprises primary germ cells and later, oogonia and oocytes. Careful and thorough investigations of morphogenesis in primordial externae support our previous results and agree with the findings of other authors.